1. Field of the Invention
The present invention relates to a picture coding/decoding, and more particularly, to a derivation process of a boundary filtering strength, a deblocking filtering method and apparatus using the derivation process.
2. Description of the Related Art
Multi-view video coding (MVC) is to process pictures of respective views obtained from a plurality of cameras, that is, to process a multi-view picture. The cameras are separated from one another in various distances and/or various directions with respect to an object according to a predetermined rule. As a result, pictures of respective views which form a multi-view picture are significantly co-related to one another. Accordingly, if such a high correlation between pictures of respective views is appropriately utilized, the coding efficiency of MVC can be substantially improved.
A research into MVC, of which standards are actively under development, is being performed to improve coding efficiency in consideration of characteristics of a multi-view picture described above on the basis of H.264/MPEG-4 part 10 advanced video coding (hereinafter, referred to as H.264/AVC) which is an international standard for motion picture coding. For example, a hierarchical B-pictures coding process, which is performed to support a temporal scalability in joint scalable video coding (JSVC) defined in H.264/AVC, is applied to an intra-view prediction coding process. In addition, in MVC, an inter-view prediction process is also performed in consideration of characteristics of a multi-view picture described above to obtain high coding efficiency.
FIG. 1 shows a prediction structure illustrating a relation between intra-view prediction and inter-view prediction in MVC of which standards are under development. FIG. 1 illustrates 8 views, which means the size of group of pictures (GOP) in a temporal direction is 8 frames. Referring to FIG. 1, S0, S1, S2, S3, . . . , S7 denote views, and T0, T1, T2, T3, . . . , T100 indicate the temporal direction.
Referring to FIG. 1, in each view, a prediction coding process is performed using a hierarchical B-picture structure defined in the H.264/AVC in a temporal direction. Pictures of each view at a first time (T0) and pictures separated from the pictures at T0 in a distance of 8 frames in the temporal direction, that is, pictures separated in a distance corresponding to the size of a group of pictures (GOP), such as pictures at T8, T16, T24, . . . , are only inter-view predicted. Specifically, at T0, T8, T16, T24, . . . , view S2 is predicted from view S0, view S1 is predicted from view S0 and view S2, view S4 is predicted from view S2, view S3 is predicted from view S2 and view S4, view S6 is predicted from view S4, view S5 is predicted from view S4 and view S6, and view S7 is predicted from view S6 since view S7 is the final view.
In every second view, that is, views S1, S3, S5, and S7, at other times T1, T2, T3 . . . T7, T9, T10 . . . temporal Intra-view prediction and inter-view prediction are performed. That is, in addition to the temporal intra-view prediction, view S1 is inter-view predicted from view S0 and view S2, view S3 is inter-view predicted from view S2 and view S4, and view S5 is inter-view predicted from view S4 and view S6.
Meanwhile, in general, light reflected from an object may differ according to an orientation, which should be considered to obtain high coding efficiency in MVC. Specifically, an object can be separated from cameras in various distances and/or various directions, and thus even when the object is pictured at identical time, pictures obtained from respective cameras can contain different brightness (also called as illumination) and/or different chrominance. In MVC of which standards are under development, after a difference in illumination and/or chrominance between pictures of respective views is compensated, inter-view prediction coding is performed to obtain high coding efficiency.
Such illumination compensation or chrominance compensation can be applied to, in addition to prediction coding in a view direction, prediction coding in a temporal direction. Prediction coding in the view direction and/or temporal direction in MVC of which standards are under development uses an illumination compensation process and/or a chrominance compensation process. In the illumination compensation process and/or the chrominance compensation process which is performed simultaneously with the motion prediction process, a illumination change value and/or a chrominance change value, which is a difference of illumination and/or chrominance between a current frame (also called as a current block) and a reference frame (also called as a reference block), is obtained and then the difference of the illumination and/or chrominance is applied to a picture of the reference frame.
However, the illumination and/or chrominance compensation process being considered in MVC of which standards are under development is performed in a block unit having a predetermined size, such as in a macroblock or a block unit smaller than the macroblock. Such an illumination compensation process and/or a chrominance compensation process in a block unit may cause blocking artifacts. Accordingly, there is a need to develop a method for eliminating or diminishing the blocking artifacts caused by illumination compensation and/or chrominance compensation. However, such a need is not considered in MVC of which standards are under development.